If 35S had been detected in the pellet instead of 32P, what would have been concluded from the Hershey-Chase experiments?

Protein is the heritable material

A fly as the following percentages of nucleotides in its DNA: 27.3% A, 27.6% T, 22.5% G, and 22.5%C. How do these numbers demonstrate Chargaff's rules?

Chagraff's rules state that in DNA, the percentages of A and T and of G and C are essentially the same, and the fly data are consistent with those rules.

How did Watson and Crick's model explain the basis for Chargaff's rules?

In the Watson-Crick model, each A hydrogen-bonds to a T, so in a DNA double helix, their numbers are equal; the same is true for G and C

In his work with pneumonia-causing bacteria and mice, Griffith found that

some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic

In analyzing the number of different bases in a DNA sample, which results would be consistent with the base-pairing rules?

A + G = C + T

DNA polymerase attaches nucleotides together. Describe this process

An anabolic reaction, creating phosphodiester bonds

What type of bond is formed between Okazaki fragments by ligase activity?

phosphodiester

Why do eukaryotic chromosomes shorten with each replication cycle? Why do bacterial chromosomes not have this problem?

Ultimately, it's because DNA Poly cannot add to the 5' end so the 5' DNA is never replaced in most cells (a shortened 5' end is produced when primers are removed).

Bacteria chromosomes are circular, so there's always a free 3' end to which DNA Polymerase can add nucleotides

What direction does DNA polymerase synthesize DNA?

5'-3' on the newly synthesized DNA

Explain how Beadle and Tatum illustrated that one gene codes for one protein. What are the exceptions to this rule?

sometimes more than one polypeptide is required to make the final protein (so more than one gene is required for a given protein), also sometimes an RNA is the final product of the gene (ex. tRNA or rRNA)

What is a codon?

a three nucleotide unit in mRNA that specifies an amino acid

The genetic code is redundant and unambiguous.Explain.

There is more than one codon per amino acid (redundant)

but each codon codes for the same amino acid each time (unambiguous)

What is a promoter? What is its purpose?

a DNA sequence that binds RNA polymerase and initiates transcription

Why is only part of the genome transcribed?

Only a subset of genes are required at any given time

How is replication and transcription similar and different?

Both use polymerases that must add nucleotides to the 3' end.

Replication and Transcription use different enzymes.

Replication duplicates DNA during S phase of the cell cycle.

Transcription makes an RNA copy of a gene.

The synthesis of proteins is endergonic or exergonic?

Endergonic

What is the third base wobble?

Pairing at the 3rd position of the codon to the anticodon isn't always strict.

Inosine in the tRNA can pair with A, C or U.

Sometimes G's pair with U's.

The 3rd base wobble is the reason we can get away with 45 tRNAs for 61 codons.

How do tRNAs become 'loaded' with their amino acids?

through the action of aminoacyl-tRNA synthetases

How are membrane proteins localized?

a signal peptide in a newly synthesized protein targets the protein to the ER lumen, where it enters the endomembrane system and from there, is targeted to the membrane

If you grow E.coli in both lactose and glucose

Cells will use glucose first

Glucose is a monosaccharide

What proteins are on the lac promoter when only lactose is present?

RNA polymerase, cAMP/CAP complex

Why does the lac operon require an activator?

because RNA polymerase doesn't stay on the DNA very well by itself, so transcription efficiency is relatively low

What is the function of B-galactosidase (B-gal)?

two functions:

a) break down lactose into glucose and galactose

b) convert lactose into allolactose by rearranging the glycosidic bonds. (B-gal carries out this second function only occasionally)

Actively transcribed genes would mostly like be....

located in euchromatin

RNAi

requires double stranded RNA

can degrade target mRNAs

Ubiquitin....

tags proteins for degradation

What genes may be on in a skin cell but off in a liver cell?

an example: the proteins that produce skin pigments (melanin) would not be on in the liver cells.

Proteins that are involved in alcohol detoxification would not be on in skin cells (at high levels)

How does the acetylation of histone tails affect gene expression?

acetylation opens up DNA, and promotes gene expression

Why would you not expect to see the same collection of activator proteins in skin and liver cells?

because activators turn on specific genes found only in certain cells

What are two ways RNAi affects gene expression?

RNAi can degrade mRNAs or prevent translation of mRNAs

What mechanism allows the cells to 'shut down' a protein once it is no longer needed?

tagging proteins with ubiquitin, which leads to protein degradation

What enzyme describes separation of the DNA strands?

Helicase

What enzyme describes requirement of a free 3'OH to synthesize new DNA?

DNA polymerase III

What enzyme describes synthesis of short segments of RNA?

primase

What enzyme describes untangling of knots?

topoisomerase

Contrast DNA replication and transcription. You must include two (2) general ways in which the process of replication and transcription differ.